Flow systems for the high-speed measurement and sorting of suspended cells is a recent, rapidly developing technology with an increasing impact on both fundamental studies in cell biology and clinical diagnostic methods. A crucial requirement is the parallel development of preparative procedures adapted to cell suspensions, to the new instruments, and to specific cytopathologic diagnostic problems such as the discrimination of normal and malignant cells. The objectives of our proposal are: 1) production of monodisperse suspensions of cells from various tissues, tumors and cultured cell sources; 2) development of methods to carry out cytochemical procedures on cells while they remain in suspension; 3) exploration of cytochemical methods oriented toward differentiation, transformation and malignancy, including DNA0and chromatin-related stains and fluorescent cell surface probes; 4) cytopathologic evaluation of the developing methods on appropriate cell model systems and clinical diagnostic problems.